The field of the invention is wireless communications. The present invention uses a mobile radio station as a measurement tool for a radio access network.
In a typical cellular radio system, a geographical area is divided into cell areas served by base stations which are connected to a radio network. Each user (mobile subscriber) in the cellular radio system is provided with a portable, pocket, hand-held, or car-mounted mobile station which communicates voice and/or data with the mobile radio network. Each base station includes a plurality of channel units including a transmitter, a receiver, and a controller and may be equipped with an omnidirectional antenna for transmitting equally in all directions or with directional antennas, each directional antenna serving a particular sector cell. Each mobile station also includes a transmitter, a receiver, a controller, and a user interface and is identified by a specific mobile station identifier.
In a cellular radio communications system, a handover operation allows an established radio connection to continue when a mobile radio participating in that connection moves between cells in the system. Handover is typically initiated when the signal strength or signal quality of the radio connection with an origination base station falls below a predetermined threshold value. Often, a low signal strength or a poor signal quality indication means that the mobile station is near a border between the two cells. If the mobile station moves closer to a destination cell or to a clearer line of unobstructed sight, handover of the radio connection to the destination cell usually results in improved radio transmission and reception.
In some cellular systems, a handover operation requires physically breaking the connection with the origination cell and then reestablishing the connection with the destination cell, i.e., a xe2x80x9cbreak-before-makexe2x80x9d switching operation. Such hard handover techniques are typically employed in Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) type cellular systems. On the other hand, xe2x80x9csoftxe2x80x9d handover techniques may be employed in Code Division Multiple Access (CDMA) type cellular systems. CDMA is an increasingly popular type of access for cellular communications because a higher spectrum efficiency is achieved compared to FDMA and TDMA techniques which means that more cellular users and/or services can be supported. In addition, a common frequency band allows simultaneous communication between a mobile station and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmit from the base stations and the mobile stations. Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal.
In CDMA, therefore, a mobile station need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a mobile station at the same time the origination cell continues to service the connection. Since the mobile station is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term xe2x80x9csoft handover.xe2x80x9d In contrast to hard handover, soft handover is a xe2x80x9cmake-before-breakxe2x80x9d switching operation.
Deciding which cells to involve in handover often requires coordination between the mobile station and the radio network. The mobile station monitors base station control or broadcast channels from adjacent cells to determine if these cells are suitable handover candidates. When suitable cell candidates are identified, the mobile station notifies the radio network of this fact which then may initiate handover operations. Of course, other handover procedures may be employed.
Power control is also important in radio communications systems, and particularly so in third generation, wideband CDMA systems (WCDMA). Before transmitting over an xe2x80x9cuplinkxe2x80x9d channel, a mobile station must set its transmission power level. Similarly, the radio access network must set base station transmit power on xe2x80x9cdownlinkxe2x80x9d channels, e.g., a paging channel, a forward access channel, traffic channels. While the actual power level set for mobile station and base station radio transmission and the interference levels that result therefrom are significant concerns in all mobile radio communications systems, such interference is particularly problematic in CDMA systems where large numbers of radio transmit and receive on the same frequency. If one station transmits at a power output that is too large, the interference it creates degrades the signal-to-interference ratio of signals received from other radio stations to the point that a receiving station cannot correctly demodulate transmissions from other radios. Another power related problem is the so-called xe2x80x9cparty effect.xe2x80x9d If a mobile transmits at too high of a power level, the other mobiles increase their respective power levels so that they can xe2x80x9cbe heardxe2x80x9d thereby compounding an already serious interference problem.
In order to effectively manage handover, power control, and other important operations in a cellular radio communications network, the network should know the current status of the network. That status can be measured reasonably well by detecting the current values of various radio-related parameters at different locations in the network. In the handover example, the radio network should know which particular cells are appropriate candidates for handover for a particular mobile station connection. With respect to another example, i.e., controlling the interference levels in a particular cell, the radio network needs to know the transmit power levels of various radios in that cell, the received power levels, interference levels, etc. Other parameters may also be desirable for the network to monitor.
While these parameters could be measured by suitably located sensors or other monitoring equipment, the cost and installation of such equipment to make it effective and worthwhile would be prohibitive. On the other hand, the mobile stations themselves could be used (secondarily) as measurement tools to provide the radio network with important measurements reflecting the stations radio environment. Those measurements could then be used to facilitate radio network operations like handover, power control, resource management, etc.
The mobile radios could periodically provide measurement reports to the radio network for a standard set of radio-related parameters. The drawback, however, with periodic measurement reports is that if the period is too long, the reports may be outdated with the radio network responding too late or too slowly to changing conditions. On the other hand, if the reporting time period is reduced to improve the relevance of the information and appropriate responsiveness of the network to changing conditions, the amount of signaling from mobile stations increases significantly. This is disadvantageous for several reasons. First, the radio bandwidth is limited, and this kind of administrative signaling creates interference and reduces capacity for user communications. Second, much of the information that is transmitted in these frequent mobile station measurement reports will likely contain the same information as in recent reports. Third, frequent reporting also drains the mobile station""s battery.
It is an object of the present invention to address the needs and overcome the problems identified above.
It is an object of the present invention to use mobile radio stations as flexible, general measurement tools for radio network control and optimization operations.
It is an object of the present invention to provide mobile station measurements in a timely, relevant fashion so that the radio network can promptly and effectively respond to changed conditions.
It is a further object of the present invention to provide the network measurement information in an efficient manner so that unnecessary measurement signaling between mobile and base station is reduced or otherwise minimized.
The present invention provides event-based or driven reporting of mobile station measurement. A mobile station measures a radio-related parameter for one or more cells in a radio access network. The mobile station evaluates the measured radio-related parameter with respect to a predetermined condition or event and determines that the predetermined condition is satisfied or that the event has occurred. Based on that evaluation, the mobile radio sends a report to the radio access network. Accordingly, the occurrence of an event and/or the satisfaction of a condition triggers the sending of the report to the network. That way the network receives the information so that it can take timely and appropriate action without sending outdated or redundant measurement reports that do not convey relevant or new measurement information.
The measurement report may identify the cell for which the mobile measurement was made, the specific triggering measurement event, the measured value of the radio-related parameter, and/or other information. The radio-related parameter may be qualitative and/or quantitative. Example parameters include signal strength, signal power, an interference level, signal-to-interference ratio, error rate, traffic volume, etc. associated with the one or more cells. Hysteresis is an additional factor that may be employed in determining whether a predetermined condition or event has occurred. A time to trigger interval may also be employed by the mobile radio in determining whether a predetermined condition is satisfied or an to event has occurred. A radio-related parameter can be evaluated with respect to two or more predetermined conditions or events with a report being sent if one or if both of the conditions are satisfied.
An example predetermined condition or event may correspond to the measured radio-related parameter moving into or moving out of a predetermined parameter range. Another example is the measured radio-related parameter for a first cell becoming better than the measured radio-related parameter for a second cell. A positive or negative offset value may be added to the measured radio-related parameter as a further required condition associated with the occurrence of an event before the measurement report is sent. That offset may vary depending on the cell. The predetermined condition or event may include a change in the measured radio-related parameter exceeding a change threshold, detection of a problem on a radio link with one of the cells, a transmit power of the mobile station crossing a threshold value, the mobile station failing to increase or decrease its transmit power on demand, and the mobile station receiver becoming saturated.
A control node in the mobile radio network instructs a mobile station to measure one or more radio-related parameters for one or more cells and to evaluate each measured radio-related parameter for each of the one or more cells with respect to a predetermined event and/or condition. The mobile station is instructed to send a report to the control node when such an event occurs. Then when the report is received from a mobile station, the controller determines whether to perform an operation based on the received report. Example operations include handover, power control, channel type switching, operation and maintenance, network balancing, network optimization, etc.
The control node provides the mobile station measurement instruction using a measurement control message that preferably includes one or more general type parameters. For example, the measurement control messages simply specify the one or more parameter measurements the mobile station is to make, identify the one or more events that can trigger a report, and what information the report should include. Because the mobile station measurements and the events are not coupled to a particular network operation or network evaluation, there is a great deal of flexibility and adaptability for future network needs and operations. In this regard, subsequent measurement control messages may modify the radio-related parameter, the predetermined event, add additional parameters to be measured, or specify other predetermined events to be evaluated. In fact, the mobile station may be instructed not to send a report even though a predetermined condition is satisfied.